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Articles avec #bio tag

#Space - Astronomers discover evidence of a "Direct-Collapse Black Hole"

7 Juillet 2016 , Rédigé par E!Sciences Publié dans #Bio

Astronomers Discover Evidence of a ‘Direct-Collapse Black Hole’

July 2016
 
CR7 Provides Evidence for an Unusual Kind of Black Hole

An image based on a supercomputer simulation of the cosmological environment where primordial gas undergoes the direct collapse to a black hole. The gas flows along filaments of dark matter that form a cosmic web connecting structures in the early universe. The first galaxies formed at the intersection of these dark matter filaments. Aaron Smith/TACC/UT-Austin

A newly published study details evidence for a direct collapse black hole in the Lyman α source CR7.

Astronomers Aaron Smith and Volker Bromm of The University of Texas at Austin, working with Avi Loeb of the Harvard-Smithsonian Center for Astrophysics, have discovered evidence for an unusual kind of black hole born extremely early in the universe. They showed that a recently discovered unusual source of intense radiation is likely powered by a “direct-collapse black hole,” a type of object predicted by theorists more than a decade ago.

 

“It’s a cosmic miracle,” Bromm said, referring to the precise set of conditions present half a billion years after the Big Bang that allowed these behemoths to emerge. “It’s the only time in the history of the universe when conditions are just right” for them to form.

These direct-collapse black holes may be the solution to a long-standing puzzle in astronomy: How did supermassive black holes form in the early epochs of the universe? There is strong evidence for their existence, as they are needed to power the highly luminous quasars detected in the young universe. However, there are several problems that should prevent their formation, and the conventional growth process is much too slow.

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#Science - Antarctic Ozone Layer shows signs of healing

7 Juillet 2016 , Rédigé par E!Sciences Publié dans #Bio

Antarctic Ozone Layer Shows Signs of Healing

 
MIT Scientists Observe First Signs of Healing in the Antarctic Ozone Layer

 

New research details the “first fingerprints of healing” of the Antarctic ozone layer.

Scientists found that the September ozone hole has shrunk by more than 4 million square kilometers — about half the area of the contiguous United States — since 2000, when ozone depletion was at its peak. The team also showed for the first time that this recovery has slowed somewhat at times, due to the effects of volcanic eruptions from year to year. Overall, however, the ozone hole appears to be on a healing path.

The authors used “fingerprints” of the ozone changes with season and altitude to attribute the ozone’s recovery to the continuing decline of atmospheric chlorine originating from chlorofluorocarbons (CFCs). These chemical compounds were once emitted by dry cleaning processes, old refrigerators, and aerosols such as hairspray. In 1987, virtually every country in the world signed on to the Montreal Protocol in a concerted effort to ban the use of CFCs and repair the ozone hole.

“We can now be confident that the things we’ve done have put the planet on a path to heal,” says lead author Susan Solomon, the Ellen Swallow Richards Professor of Atmospheric Chemistry and Climate Science at MIT. “Which is pretty good for us, isn’t it? Aren’t we amazing humans, that we did something that created a situation that we decided collectively, as a world, ‘Let’s get rid of these molecules’? We got rid of them, and now we’re seeing the planet respond.”

Solomon’s co-authors include Diane Ivy, research scientist in the Department of Earth, Atmospheric and Planetary Sciences, along with researchers at the National Center for Atmospheric Research in Boulder, Colorado, and the University of Leeds in the U.K.

 

Signs before spring

The ozone hole was first discovered using ground-based data that began in the 1950s. Around the mid-1980s, scientists from the British Antarctic survey noticed that the October total ozone was dropping. From then on, scientists worldwide typically tracked ozone depletion using October measurements of Antarctic ozone.

Ozone is sensitive not just to chlorine, but also to temperature and sunlight. Chlorine eats away at ozone, but only if light is present and if the atmosphere is cold enough to create polar stratospheric clouds on which chlorine chemistry can occur — a relationship that Solomon was first to characterize in 1986. Measurements have shown that ozone depletion starts each year in late August, as Antarctica emerges from its dark winter, and the hole is fully formed by early October.

Solomon and her colleagues believed they would get a clearer picture of chlorine’s effects by looking earlier in the year, at ozone levels in September, when cold winter temperatures still prevail and the ozone hole is opening up. The team showed that as the chlorine has decreased, the rate at which the hole opens up in September has slowed down.

“I think people, myself included, had been too focused on October, because that’s when the ozone hole is enormous, in its full glory,” Solomon says. “But October is also subject to the slings and arrows of other things that vary, like slight changes in meteorology. September is a better time to look because chlorine chemistry is firmly in control of the rate at which the hole forms at that time of year.  That point hasn’t really been made strongly in the past.”

 

A healing trend

The researchers tracked the yearly opening of the Antarctic ozone hole in the month of September, from 2000 to 2015. They analyzed ozone measurements taken from weather balloons and satellites, as well as satellite measurements of sulfur dioxide emitted by volcanoes, which can also enhance ozone depletion. And, they tracked meteorological changes, such as temperature and wind, which can shift the ozone hole back and forth.

They then compared their yearly September ozone measurements with model simulations that predict ozone levels based on the amount of chlorine that scientists have estimated to be present in the atmosphere from year to year. The researchers found that the ozone hole has declined compared to its peak size in 2000, shrinking by more than 4 million square kilometers by 2015. They further found that this decline matched the model’s predictions, and that more than half the shrinkage was due solely to the reduction in atmospheric chlorine.

“It’s been interesting to think about this in a different month, and looking in September was a novel way,” Ivy says. “It showed we can actually see a chemical fingerprint, which is sensitive to the levels of chlorine, finally emerging as a sign of recovery.”

The team did observe an important outlier in the trend: In 2015, the ozone hole reached a record size, despite the fact that atmospheric chlorine continued to drop. In response, scientists had questioned whether any healing could be determined. Going through the data, however, Solomon and her colleagues realized that the 2015 spike in ozone depletion was due primarily to the eruption of the Chilean volcano Calbuco. Volcanoes don’t inject significant chlorine into the stratosphere but they do increase small particles, which increase the amount of polar stratospheric clouds with which the human-made chlorine reacts.

“Why I like this paper so much is, nature threw us a curveball in 2015,” says Ross Salawitch, professor of chemistry and biochemistry at the University of Maryland. “People thought we set a record for the depth of the ozone hole in October 2015. The Solomon paper explains it was due to a specific volcanic eruption. So without this paper, if all we had was the data, we would be scratching our heads — what was going on in 2015?”

As chlorine levels continue to dissipate from the atmosphere, Solomon sees no reason why, barring future volcanic eruptions, the ozone hole shouldn’t shrink and eventually close permanently by midcentury.

“What’s exciting for me personally is, this brings so much of my own work over 30 years full circle,” says Solomon, whose research into chlorine and ozone spurred the Montreal Protocol. “Science was helpful in showing the path, diplomats and countries and industry were incredibly able in charting a pathway out of these molecules, and now we’ve actually seen the planet starting to get better. It’s a wonderful thing.”

This research was supported, in part, by the National Science Foundation and the U.S. Department of Energy.

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#Climate - Climat's coral killers move in swiftly

3 Juillet 2016 , Rédigé par E!Sciences Publié dans #Bio

Climate’s coral killers move in swiftly

June 23, 2016, by Tim Radford

CROP-- Bleached reef

Desolate seascape of bleached corals on the Great Barrier Reef off the coast of Queensland.
Image: John Howell via Flickr

 
 

Worst-ever bleaching event affects 93 percent of the Great Barrier Reef as rising temperatures and sea levels bring swift death to vast swathes of colourful corals.

 

LONDON, 23 June, 2016 – Corals affected by mass bleaching on the northern Great Barrier Reef are “the sickest” Australian scientists have ever seen.

The corals have been hit by unusually high sea temperatures – a consequence of El Niño, the periodic blister of heat that bubbles up in the Pacific and started in full force last year.

Corals thrive in tropic seas, but, like all animals, there is a limit to their heat tolerance. And in a year in which global temperatures each month have set new all-time records, even the corals are feeling the heat, scientists told this week’s 13th International Coral Reef Symposium in Honolulu, Hawaii.

Terry Hughes, director of the ARC Centre of Excellence for Coral Reef Studies (CoralCoE) at James Cook University in Queensland, said: “We measured the condition of surviving corals as part of our extensive underwater surveys of Australia’s worst-ever bleaching event. We found that coral bleaching has affected 93% of the Great Barrier Reef.

 

Counteract damage

“While the central and southern regions have escaped with minor damage, nearly half of the corals have been killed by mass bleaching in the northern region.”

His CoralCoE colleague, Bill Leggat, head of the Symbiosis Genomics Research Group, said: “Normally, when bleaching kills corals it is a slow death that progresses steadily when temperatures remain high. The corals usually rely on mechanisms that help them fight and counteract the damage. But this time, on some reefs, it looks like they have died very quickly.”

Coral and algae called zooxanthellae live in a mutual help relationship. The algae harness the light to make nutrients that nourish the coral host, and they also give the corals the pattern of colours that make the reefs such a marvel.

But as temperatures soar beyond the coral comfort zone, the relationship breaks down. Where a healthy coral polyp might have up to two million zooxanthellae per square centimetre, numbers may drop to 200,000 in a bleaching event.

But this time, at least in the northern end of the reef, conditions are much worse. Some corals have almost no algal partners left.

 

“These corals are among the most damaged I have seen,” Dr Leggat said. “For some surviving corals in the northern Great Barrier Reef, over 50% of the coral cells are dead. In some regions, the corals were so badly damaged that we were unable to study their tissue because it was rotting away.”

 

“It’s time to shift this conversation to what can be done to conserve these amazing organisms . . . local conservation buys us time, but it isn’t enough”

 

Bleaching and devastation were first reported last year. Coral is already threatened by insidious change in sea water chemistry as ever more carbonic acid – from dissolved atmospheric carbon dioxide, the product of the combustion of fossil fuels – gets into the sea.

Rising sea levels also present a problem. Researchers believe that the loss of the Bramble Cay melomys, a rodent native to the reef, could be counted as the first real mammal extinction laid directly at the door of climate change. Reefs normally support rich and complex ecosystems, but when the reef suffers, so do all the creatures that make their homes in the corals.

Coral reefs have been hit by massive bleaching events in the past, and recovered. But this event seems more sustained. A new report from the US National Oceanic and Atmospheric Administration (NOAA) suggests that many coral reefs will be exposed to higher-than-normal sea temperatures for the third year in a row, with damage to reefs in Hawaii, Guam, the northern Mariana islands, the Florida Keys, the US Virgin Islands and Puerto Rico.

“It’s time to shift this conversation to what can be done to conserve these amazing organisms in the face of this unprecedented global bleaching event,” says Jennifer Koss, coral reef conservation programme director at the NOAA.

“We have boots on the ground and fins in the water to reduce local stressors. Local conservation buys us time, but it isn’t enough. Globally, we need to better understand what actions we all can take to combat the effects of climate change.”

 

Combination punch

Even so, there is some hope. A study backed by 35 scientists reporting for the UN Environment Programme says that reefs nearest the surface along the full length of the Great Barrier have been affected by the combination punch of global warming and the extremes of El Niño.

But it says that deeper reef environments – 40 metres to 150 metres below the waves – could serve as a refuge for species driven from the shallows, although more research needs to be done to establish a role for these regions.

“They aren’t a silver bullet, but they may be able to resist the most immediate impacts of climate change – thereby providing a refuge for some species and potentially helping to replenish destroyed surface reef and fish populations,” says Professor Elaine Baker, a senior expert at of the University of Sydney’s school of geosciences. – Climate News Network

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